Power supply device for vehicle

ABSTRACT

A vehicle power supply device converts power from high voltage to low voltage by selectively connecting a predetermined power storage element group to a low voltage electric load from a high voltage power supply formed by connecting power storage elements in series. A leakage resistance from the high voltage power supply to the ground is measured when the high voltage circuit is cut by the cutoff means placed between the high voltage power supply and the high-voltage load device. When the value less than a predetermined value, the connection between the high voltage power supply and the low-voltage load device is interrupted, so that electric shock is prevented.

TECHNICAL FIELD

The present invention relates to a power supply device mounted on avehicle. The power supply device includes a high-voltage power storagemeans particularly used for vehicle traveling and the like, and alow-voltage power supply for supplying an electric load other than thatfor a vehicle traveling. The power supply device is configured to obtainthe low voltage power supply from the high-voltage power storage meansvia a step-down means.

BACKGROUND ART

As the power supply device, a vehicle power supply device according tothe proposal of the present applicant is known (Patent Publication (1)).In this vehicle power supply device, the high voltage power supply isformed by connecting power storage elements in series. The vehicle powersupply device performs power conversion from a high voltage to a lowvoltage by selectively connecting a predetermined power storage elementgroup to a low voltage electric load. The vehicle power supply deviceswitches the power storage element group at high speed to make theswitching loss of the switching means almost zero.

PRIOR ART PUBLICATION Patent Publication

-   [Patent Publication (1)] Japanese Laid-Open Patent Publication No.    2018-26973

SUMMARY OF THE INVENTION Problem(s) to be Solved by the Invention

There are various embodiments of the electric power storage means fordriving the vehicle from a low voltage of about 48 V to a system using ahigh voltage of about 600 V. Generally, a vehicle using a voltageexceeding 60 V is provided with a configuration for preventing anelectric shock accident. This prevents an electric shock accident whenthe human body touches the electric circuit portion connected to thepower storage means of the vehicle.

Therefore, in a general high voltage system of a vehicle, a DC-DCconverter provided with an isolation transformer is arranged between thehigh voltage part and the low voltage part as shown in FIG. 1 . At thesame time, the high voltage circuit floats both the negative potentialcircuit and the positive potential circuit while avoiding directconnection with the vehicle body. With this configuration, even if thehuman body touches any part of the circuit portion including the highvoltage power storage means, no electric shock is caused.

Here, according to Patent Publication (1), the low potential side of theload means 50, which is a low voltage circuit, is generally connected tothe vehicle body as a body ground of a 12V power supply. When any one ormore of the switch means (30 to 35) is closed, any of the connectionpoints of the power storage means (20 a to 20L) connected in series onthe high voltage side is directly connected to the vehicle body.Therefore, if the human body touches the high voltage circuit, anelectric shock will occur. Specifically, it is assumed that the totalseries voltage of the power storage means (20 a to 20L) is 480V. Whenthe human body touches the positive potential side of the power storagemeans 20 a and the vehicle body at the moment when the switch means 35is closed, a high voltage of 480 V is applied to the human body. It ispossible that an electric shock accident may occur.

The present invention has been made in view of the above problems. Thiscan be applied to a case where a vehicle power supply device mounted ona vehicle and obtaining a low voltage power supply from a high voltagepower supply via a step-down means is configured as a system having avoltage exceeding 60 V on the high voltage power supply side. 60V is thevoltage of the electric shock limit of the human body. Even in thiscase, it is possible to prevent an electric shock accident without usingan insulating means such as a transformer. Further, the presentinvention provides a power supply device for a vehicle that easilyobtains a power conversion efficiency of about 100% in a powerconversion function to the low voltage side.

Solution(s) to the Problem(s)

The present invention described in Claim 1 is a power supply device fora vehicle, comprising: an electric load that operates at a predeterminedlow voltage; a high-voltage power supply that provides a high-voltage DCpower supply by connecting in series a plurality of power storageelements constituting nodes that supply said predetermined low voltage;a high-voltage load device connected to the high-voltage power supplyvia a wire harness; a plurality of switch means provided correspondingto said nodes that supply the predetermined low voltage to the electricload; a control means wherein the control means supplies a voltage byturning on one of the switch means for supplying the voltage from atleast one node and turning off the other switch means for supplying thevoltage from the other nodes, and after setting a dead time period toturn off all the switch means once, by sequentially repeating turning ona next one of the switch means of a next node that supplies the voltagenext and turning off the other switch means that supply the voltage fromthe other nodes so that the voltage is supplied from all the storageelements; a cutoff means for cutting off an electric circuit between thehigh-voltage power supply and the high-voltage load device; and aleakage detection means that detects a leakage resistance between anelectric circuit part constituting the high-voltage power supply and thehigh-voltage load device and a ground potential and sends a signal tosaid control means, wherein the control means determines the signaltransmitted from the leakage detection means during the period when thecutoff means is off, and when the leakage resistance is equal to orlower than a predetermined value, all the switch means are kept an offstate for a predetermined period of time.

The present invention described in Claim 2 is a power supply device fora vehicle, wherein in said high-voltage power supply, (n (n: naturalnumber)×N (N: natural number)) of said power storage elementsconstituting the nodes, in which n pieces of the nodes make up thepredetermined low voltage, are connected in series, and a DC powersource having a high voltage N times higher than the predetermined lowvoltage can be obtained.

The present invention described in Claim 3 is a power supply device fora vehicle, wherein said control means controls the switch means so as toperiodically change a plurality of selected nodes.

The present invention described in Claim 4 is a power supply device fora vehicle, wherein said control means determines a node to be selectedso that charge/discharge states of the plurality of power storageelements become substantially uniform.

The present invention described in Claim 5 is a power supply device fora vehicle, wherein said control means determines a selective holdingtime of each node so that charge/discharge states of the plurality ofpower storage elements become substantially uniform.

The present invention described in Claim 6 is a power supply device fora vehicle, wherein a time for connecting said high-voltage power supplyto said high-voltage load device by said cutoff means is set so that atime during which the current flows from the high voltage power supplyto a human body is less than a time during which an electric shockaccident is caused in the human body.

The present invention described in Claim 7 is a power supply device fora vehicle, wherein said time for connecting said high-voltage powersupply to said high-voltage load device by said cutoff means is set soas to be a time which is inversely proportional to a voltage value ofthe high voltage power supply, or a time which is proportional to theleakage resistance value detected by the leakage detecting means.

The present invention described in Claim 8 is a power supply device fora vehicle,

wherein said control means fixes all the switch means to the off statewhen a leakage resistance value of said leakage detection means is equalto or lower than a predetermined value.

The present invention described in Claim 9 is a power supply device fora vehicle,

wherein when a leakage resistance value of the leakage detection meansis equal to or lower than a predetermined value, said control meansholds a state in which all the switch means are off for a predeterminedtime and subsequently repeats an operation for connecting said each nodeand said electric load by the switch means.

The present invention described in Claim 10 is a power supply device fora vehicle, wherein when a leakage resistance value of the leakagedetection means is equal to or lower than a first threshold value, saidcontrol means turns off the switch means, when a leakage resistancevalue of the leakage detection means is equal to or higher than a secondthreshold value which is larger than the first threshold, said controlmeans repeats an operation of a state in which the switch means is on.

The present invention described in Claim 11 is a power supply device fora vehicle, wherein said control means controls said cutoff means so thata product of a period in which said high-voltage power supply and saidhigh-voltage load device are connected and the current flows from thehigh voltage power supply to a human body is 0.003 amperes×1 second orless.

The present invention described in Claim 12 is a power supply device fora vehicle, wherein said control means sets a cycle for switching a nodeselected by said switch means to be a predetermined value or less sothat a magnitude of a charge/discharge depth in each node of the powerstorage element is equal to or less than a predetermined value.

The present invention described in Claim 13 is a power supply device fora vehicle, wherein a low voltage capacitor is connected in parallel withthe electric load.

The present invention described in Claim 14 is a power supply device fora vehicle, wherein a high voltage capacitor is connected in parallelwith said high-voltage load device.

The present invention described in Claim 15 is a power supply device fora vehicle, wherein said dead time period or a capacitance value of thelow voltage capacitor is set so that a voltage drop width applied to theelectric load during the dead time period is not more than apredetermined value.

The present invention described in Claim 16 is a power supply device fora vehicle, wherein an off period of said cutoff means or a capacitancevalue of the high voltage capacitor is set so that a voltage drop widthapplied to the high-voltage load device during the off period of saidcutoff means is not more than a predetermined value.

The present invention described in Claim 17 is a power supply device fora vehicle, wherein the capacitor is arranged in parallel with each nodeof said power storage element.

The present invention described in Claim 18 is a power supply device fora vehicle, wherein from each node of the high-voltage power source thatprovides said high-voltage DC power supply by connecting in series saidpower storage elements, an AC power is supplied to the electric load byalternately reversing a polarity with a high potential side and a lowpotential side at predetermined periods when the electric load isconnected by the switch means.

Effect(s) of the Invention

The vehicle power supply device described in Claim 1, Claim 2, assumingthat the voltage of the low voltage power supply is [Vt.], the voltage[VH] of the high voltage power supply to which the power storageelements are connected in series is VL×N (N is a natural number).Moreover, since the number of the power storage elements is N×n (n is anatural number), for example, when [VL] is 12V and N=40, [VH] is 480V.Assuming that n=4, a high voltage power supply is composed of a total ofN× n=160 power storage elements in series. The voltage of each powerstorage element is 3V.

Therefore, in order to obtain a low voltage power supply of 12V, fourpower storage elements connected in series may be selected in a groupmanner and connected to an electric load.

However, in order to obtain a 12V low voltage power supply from a 480Vhigh voltage power supply, it is not necessary to use a DC-DC converterusing a known switching power supply circuit or the like. Step-down canbe realized by a simple switch means that selectively connects to anelectric load from each node (group node) of the power storage elementconnected in series.

Therefore, the configuration of the switch means can be simplified.Since the known switching loss and the loss generated from the inductorcan be significantly reduced, the power loss for step-down can bereduced and the heat dissipation structure can be simplified. As aresult, the weight and cost of the power supply device including thedevice for such step-down can be reduced.

Here, a part of the nodes of the power storage element connected inseries of the high voltage power supply is connected to the low voltagecircuit, that is, the metal part of the vehicle body via the switchmeans. When a human touches the high voltage power supply circuit part,an electric shock current flows through the human body.

However, the control means periodically turns off the cutoff means anddetects the ground fault current flowing from the high-voltage circuitportion connected to the outside of the vehicle power supply device asthe leakage resistance value by the leakage detection means. When thevalue is equal to or lower than a predetermined value, judged as thehuman body is touched to the high voltage circuit, the switching meansis turned off and the connection between the high-voltage power supplyand the low-voltage circuit, that is, the metal part of the car body iscut off, the electric shock accident is prevented by blocking theenergization to the human body due to the contact between the car bodyand the high-voltage power supply.

The vehicle power supply device described in Claim 2, in the highvoltage power supply, a plurality of power storage elements constitutinga node having a predetermined low voltage with n (n: natural number) areconnected in series (n×N (N: natural number)). A DC power supply havinga high voltage N times a predetermined low voltage is obtained.Therefore, it is possible to efficiently supply a high voltage and apredetermined low voltage by using all the power storage elements.

The vehicle power supply device described in Claim 3, the control meansperiodically changes the node selected by the switch means from theplurality of power storage elements. Among the power storage elementsconnected in series, it is possible to prevent a problem that only apart of the power storage elements is discharged and the other powerstorage elements are overcharged.

The vehicle power supply device described in Claim 4, the control meansdetermines the node to be selected so that the charge/discharge statesof the plurality of power storage elements are substantially uniform. Italso has a known cell balance function required when charging anddischarging a plurality of power storage elements in series.

The vehicle power supply device described in Claim 5, the control meansdetermines the selective holding time of each node so that thecharge/discharge states of the plurality of power storage elementsbecome substantially uniform. The selective holding time of each node isdetermined so that the charge/discharge state of the plurality of powerstorage elements becomes substantially uniform and the discharge time islong for the node selected from the power storage elements having alarge charge amount. On the contrary, the selective holding time of eachnode is determined so that the discharge time is short for the nodeselected from the power storage elements having a small charge amount.It also has a known cell balance function required when charging anddischarging a plurality of power storage elements in series.

It is said that when a high voltage is applied to the human body, thereis no effect on the human body if the current value is 5 mA or less. Itis known that in a current range larger than this, the human bodyreaction changes depending on the duration. As the current valueincreases, the human body is damaged by electric shock in a short time.

Therefore, in the earth-leakage circuit breaker used for a generalcommercial power supply, the earth-leakage detection sensitivity of 30mA×0.1 sec is set.

The vehicle power supply device described in Claim 6, the control meanssets the period for connecting the high-voltage power source to thehigh-voltage load device by the cutoff means to be less than the timeduring which an electric shock accident occurs in the human body. Thisperiod is the duration of the leakage current flowing from the highvoltage power supply to the human body. Even when a person touches acircuit part of a high voltage power supply, it is possible to eliminatethe damage to the human body.

The vehicle power supply device described in Claim 7, the time forconnecting the high-voltage power supply to the high-voltage load deviceby the cutoff means is set so as to be a time which is inverselyproportional to a voltage value of the high voltage power supply, or atime which is proportional to the leakage resistance value detected bythe leakage detecting means. When the voltage value of the high-voltagepower supply or the resistance value generated between the ground andthe human body becomes small and the electric shock current of the humanbody becomes large, the energization time to the human body, that is,the electric shock time can be shortened, so that the safety is furtherimproved.

The vehicle power supply device described in Claim 8, the control meansfixes the switch means to the off state when a leakage resistance valueof said leakage detection means is equal to or lower than apredetermined value. By cutting off the electric circuit that connectsthe high-voltage power supply and the vehicle body, it is possible toprevent electric shock accidents by blocking the energization of thehuman body due to contact between the vehicle body and the high-voltagepower supply, which is safer.

The vehicle power supply device described in Claim 9, when a leakageresistance value of the leakage detection means is equal to or lowerthan a predetermined value, the control means holds a state in which theswitch means is off for a predetermined time, for example 0.5 second,and subsequently repeats an operation of a state in which the switchmeans is on. Ensure safety by giving a sufficient pause time to theelectric shock to the human body. Even if a temporary leakage currentoccurs due to a failure of each part of the vehicle body, the powersupply from the high voltage power supply to the low-voltage load deviceis resumed, so that the vehicle function can be maintained.

The vehicle power supply device described in Claim 10, when a leakageresistance value of the leakage detection means is equal to or lowerthan a first threshold value, for example, 10 kiloohms, the controlmeans turns off the switch means, when a leakage resistance value of theleakage detection means is equal to or higher than a second thresholdvalue, for example, 100 kiloohms, the control means repeats an operationof a state in which the switch means is on. If the detection resistancevalue is small and the electric shock current overs to a safe value,disconnect the connection between the high voltage power supply and lowvoltage circuit. If the resistance value is large and the electric shockcurrent drops to the safe value, reconnect the connection. The safety ofthe human body is ensured, and even if a temporary leakage currentoccurs due to a failure of each part of the vehicle body, the powersupply from the high voltage power supply to the voltage load device isresumed, so that the vehicle function can be maintained.

The vehicle power supply device described in Claim 11, the control meanscontrols the cutoff means so that the product of the period forconnecting the high voltage power supply and the high-voltage loaddevice and the electric shock current value of the human is 0.003amperes×1 second or less. It is possible to secure the same level ofsafety as the standard 0.03 amps×0.1 seconds or less of theearth-leakage circuit breaker used in general commercial power supplies.

The vehicle power supply device described in Claim 12, the control meanssets a cycle for switching the node selected by the switch means so thatthe magnitude of the charge/discharge depth at each node of the powerstorage element is equal to or less than a predetermined value. It ispossible to minimize the decrease in the life of each power storageelement due to the charging/discharging depth of each power storageelement being too large.

The vehicle power supply device described in Claim 13, the control meanspowers the switch means from the low voltage capacitor during aso-called dead time period that disconnects the connection between allthe nodes and the electrical load. As a result, it is possible toprevent the voltage supplied to the electric load from dropping. Thevoltage supplied to the electric load can be kept stable.

The vehicle power supply device described in Claim 14, the control meanspowers the high-voltage load device from the high voltage capacitorduring the cutoff means off. As a result, it is possible to prevent thevoltage supplied to the high-voltage load device from dropping. Thevoltage supplied to the high-voltage load device can be kept stable.

The vehicle power supply device described in Claim 15, since the voltageapplied to the electric load before and after the switch means isswitched can be maintained, the potential difference between both endsof the switch means immediately before the switch means is turned on canbe eliminated, and the switching loss can be eliminated.

The vehicle power supply device described in Claim 16, since the voltageapplied to the electric load before and after the cutoff means isswitched can be maintained, the potential difference between both endsof the cutoff means immediately before the switch means is turned on (orturned off) can be eliminated, and the switching loss can be eliminated.

Next, if the internal resistance of the power storage element is largeimmediately after the switch means switches the connection to anarbitrary node, it takes a lot of time to charge the capacitor connectedin parallel with the electric load. Therefore, it is inevitable that thevoltage supplied to the electric load will drop at the timing when theswitch means is switched.

The vehicle power supply device described in Claim 17, a capacitor witha small internal impedance is placed in parallel with the series node ofthe power storage element. Immediately after the switch means switchesthe connection to any node, the capacitor can be charged with asufficiently small power supply impedance, that is, a large current. Itis possible to suppress a decrease in the voltage supplied to theelectric load.

The vehicle power supply device described in Claim 18, power is suppliedfrom each node of a high voltage power supply that obtains ahigh-voltage DC power supply by connecting a plurality of power storageelements in series. The polarities of the high-potential side and thelow-potential side, when connected to the electric load by the switchmeans, are alternately reversed at predetermined intervals. AC power issupplied to the electric load. AC power can be supplied from the vehiclefor the use of household appliances that require commercial power.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a diagram showing a basic configuration of a general vehiclepower supply device;

FIG. 2 a diagram showing a basic configuration of a vehicle power supplydevice according to an embodiment of the present invention;

FIG. 3 a timing chart showing the basic operation of the vehicle powersupply device according to the embodiment of the present invention;

FIG. 4 a diagram illustrating electric shock prevention method of avehicle power supply device according to the embodiment of the presentinvention;

FIG. 5 a diagram illustrating electric shock prevention method of avehicle power supply device according to the embodiment of the presentinvention;

FIG. 6 a diagram illustrating electric shock prevention method of avehicle power supply device according to the embodiment of the presentinvention;

FIG. 7 a diagram showing a configuration for measuring the voltage ofeach node of the power storage element;

FIG. 8 a diagram showing the selective holding time of each node;

FIG. 9 a diagram showing an embodiment of a vehicle power supply deviceaccording to the embodiment of the present invention;

FIG. 10 a diagram illustrating power loss of a switching element;

FIG. 11 a diagram illustrating power loss of a switching element;

FIG. 12 a diagram illustrating the charge/discharge depth of the powerstorage element;

FIG. 13 a diagram showing another embodiment of the vehicle power supplydevice according to the embodiment of the present invention;

FIG. 14 a diagram illustrating a method of supplying AC power to anelectric load; and

FIG. 15 a diagram showing a configuration to boost the voltage of thepower storage element according to the embodiment of the presentinvention.

MODE TO CARRY OUT THE INVENTION Embodiment

Hereinafter, embodiments of the vehicle power supply device of thepresent invention will be described with reference to Figs. FIG. 2 is abasic embodiment of the present invention. A vehicle power supply device1 includes power storage elements (1 a to 40 d) constituting a secondarybattery charged by a power generation means (not shown) mechanicallyconnected to a drive mechanism mounted on the vehicle and traveling byan engine and a motor. The vehicle power supply device 1 includesswitching means (S1 a to S40 b), control means 200, leakage detectionmeans 100, and cutoff means 500, 501. The vehicle power supply device isconnected to electric load 300 which is operated by 12V, and one end onthe negative potential side is electrically connected to the vehiclebody. The vehicle power supply device 1 is connected to the high voltageload device 400 via the wire harnesses W1 and W2, and supplies theelectric power of the high voltage power storage elements 1 a to 40 d tothe high voltage load device 400.

In FIG. 2 , the power storage elements (3 b to 39 d), the switchingmeans (S3 b to S39 a) connected to the power storage elements, and theparts where the switching means and the control means 200 are connectedare omitted.

The power generation means is driven by an engine (not shown) in orderto supply the electric power required for the vehicle electricalcomponents. The power generation means is configured to regenerate thekinetic energy at the time of deceleration via the drive mechanism atthe time of deceleration of the vehicle and charge the power storageelement (1 a to 40 d).

Each node of the power storage element (1 a to 40 d) is, for example, alithium ion battery having a charging voltage of 3V. All the nodes ofthe power storage element (1 a to 40 d) are connected in series. A highvoltage power supply with a total of 480 V is formed, where 40 is amultiple N with respect to the required voltage of 12 V of the electricload 300. The high voltage power supply powers the electric drivecontrol system. The electric drive control system is composed of anin-vehicle motor, an inverter (not shown), etc. The high voltage powersupply acts to assist the driving torque of the engine. As a result,when the vehicle is power running, the energy regenerated duringdeceleration can be reused for traveling, so that it is possible toimprove the traveling fuel efficiency of the vehicle.

In the power storage elements (1 a to 40 d), the nodes 1 a to 1 d areconfigured as the first group node, the nodes 2 a to 2 d are configuredas the second group node, and the nodes 3 a to 3 d are configured as thethird group node. Then, the nodes 40 a to 40 d are configured as the40th group node. Switching means (S1 a to S40 b) are connected to bothends of each group node.

The total number of nodes of the power storage elements (1 a to 40 d) isN×n=160 in total by multiplying the multiple N=40 by the number n=4 ineach group node. In the claims, group nodes may simply be referred to asnodes.

Here, the total voltage of the power storage elements in series in eachof the first to 40th group nodes is 3V×4=12V.

As shown in FIG. 2 , the control means 200 controls the ON/OFF state ofthe switching means (S1 a to S40 b) and the ON/OFF state of the cutoffmeans 500, 501.

As shown in FIG. 3 , the control means 200 turns on the switching means(S1 a, S2 a) and connects the electric load 300 and the first group nodeof the power storage element for [Ton] time, for example 10milliseconds. At this time, the switching means other than the switchingmeans (S1 a, S2 a) are turned off. The switching means S2 a is connectedto the positive electrode side of the first group node, and theswitching means S1 a is connected to the negative electrode side of thefirst group node. Therefore, a DC voltage of 12 V is applied to theelectric load 300 for [Ton] time.

Next, the control means 200 keeps all the above-mentioned switchingmeans (S1 a to S40 b) OFF during the period [Td] shown in FIG. 3 . Thereason why the period [Td] is provided is that, for example, when theswitching means S1 a and the switching means S1 b are turned on at thesame time, an excessive current flows in the closed circuit. The closedcircuit is formed by the switching means Sla, the switching means S1 b,and the nodes (1 a, 1 b, 1 c, 1 d) of the power storage element. This isbecause the switching means may be damaged or the charging power of eachpower storage element may be wasted.

It is assumed that, for example, a known MOSFET is adopted as theswitching means (S1 a to S40 b). It is known that when a signal forcontrolling ON/OFF of each switching means is transmitted from thecontrol means 200, a time delay occurs until the switching means (S1 ato S40 b) actually respond. Therefore, the control means 200 requires asufficient waiting time [Td] from turning off the desired switchingmeans to turning on the other switching means. This [Td] is called deadtime. In the case of a general MOSFET, the dead time needs to be severaltens of nsec to several nsec.

As described above, the control means 200 turns on the switching means(S1 a, S2 a) for the first group node of the power storage elementduring [Ton], and connects the first group node to the electric load300. As a result, the required voltage of 12V is supplied to theelectric load 300. Subsequently, for the second group node, the secondgroup node is connected to the electric load 300 during [Ton] via theswitching means (S1 b, S3 a). For the third group node, the third groupnode is connected to the electrical load 300 during [Ton] via theswitching means (S2 b, S4 a). Finally, for the 40th group node, the 40thgroup node is connected to the electrical load 300 during [Ton] via theswitching means (S39 b, S400. In this way, [T] (Ton time 10 ms×number ofgroup nodes 40=0.4 seconds) shown in FIG. 3 is repeated as one cycle,and the supply of 12 V DC power to the electric load 300 is continued.The charge/discharge state of each of the first to 40th power storageelement group nodes can be kept substantially uniform.

Next, FIGS. 2 and 4 will be referred to, and the operation of theleakage detecting means 100 will be explained.

The leakage detecting means 100 is connected to the high voltage circuitpart by the wire harnesses W1 and W2 extending to the outside of thevehicle power supply via the terminal T102 and the terminal T101, and isgrounded to the vehicle body via the terminal T103. Here, the earthleakage detecting has not shown inside power source. The earth leakagedetecting means compares the current flowing between the terminal T101and the grounding terminal T103 with the current flowing between theterminal T102 and the grounding terminal T103, and measures theelectrical resistance value there between. The earth leakage detectingmeans is configured to output a smaller resistance value to the controlmeans 200.

During the period when the cutoff means 500 and 501 are off, theterminal T101 and the terminal T102 of the leakage detection means 100are floating with respect to the vehicle body, so that the leakageresistance value is substantially infinite. However, when a human bodytouches the high voltage circuit portion on the wire harness W1 side, arelatively small resistance value is detected between the terminal T101and the ground terminal T103 because the resistance value of the humanbody is about 5 KΩ.

As shown in FIG. 4 , the control means 200 repeats the operation in theperiod TS for turning on the blocking means 500 and 501 for the TNperiod and turning off the TF1 (TF2) period. During the period when thecutoff means 500 and 501 are on, the high voltage power supply by thepower storage element 1 a to 40 d is supplied to the high voltage loaddevice 400. During the period when the cutoff means 500 and 501 are off,the high voltage circuit portions connected to the outside by the wireharnesses W1 and W2 connected to the outside from the vehicle powersupply device 1 are cut off and the high voltage circuit portion is in afloating state.

Therefore, the leakage resistance value [RLeak] of the leakage detectionmeans 100 in the period TF1 shown in FIG. 4 is infinite. However, sincethe human body is in contact with the high voltage circuit portionoutside the vehicle power supply device during the period TF2, theleakage resistance value [RLeak] detected by the leakage detection means100 is a relatively small value.

The control means 200 inputs the leakage detection value [ILeak] to theterminal T200 of the control means 200 via the terminal T100 of theleakage detection means 100. When the control means 200 detects that the[ILeak] is equal to or lower than the predetermined value [RLth], thecontrol means 200 fixes the switch means (S1 a to S40 b) to the offstate, as shown in FIG. 4 .

Alternatively, as shown in FIG. 5 , the control means 200 set the[Thold], for example, about 0.5 seconds, off the switch means (S1 a toS40 b) and the switch means (S1 a to S40 b) may repeat an operation forconnecting each group node.

As shown in FIG. 5 , the control means 200 turns off the switch means(S1 a to S40 b) for the period [Thold] in the off-cycle [TF2] of thecutoff means 500 and 501, when the leakage resistance value [RLeak] isthe threshold value [RLth] or less, it is determined that the human bodyis in contact with the high voltage circuit.

Next, the control means 200 selectively connects the group nodes in theorder to be selected next to the group note selected during the period[TF2] among the switching means S1 a to S40 b, for example, turns on S2b and S4 a.

Subsequently, the control means 200 turns keeps off all the switch meansincluding the switch means S2 b, s4 a for the period [Thold] in theoff-cycle [TF3] of the cutoff means 500 and 501, when the leakageresistance value [RLeak] is the threshold value [RLth] or less, it isdetermined that the human body is still in contact with the high voltagecircuit, and repeats on and off in a cycle of about 0.5 seconds

In the off-cycle [TF*] (* is optional) of the cutoff means 500 and 501,when the leakage resistance value [RLeak] is the threshold value [RLth]or more, it is determined that the human body is not in contact with thehigh voltage circuit, the switching means S1 a to S40 b are sifted to onstate and the operation that the voltage of the group nodes selectivelysupplied to the low voltage electric load 300 is resumed.

As yet another embodiment, as shown in FIG. 6 , when the control means200 detects that the leakage resistance value [RLeak] is equal to orless than the first threshold voltage [RLth1] in the off period TF2 ofthe cutoff means 500 and 501, the switching means (S1 a to S40 b) isturned off, and then the leakage resistance value [RLeak] is still equalto or less than the first threshold [RLth1] in the next period [TF3],the switching means (S1 a to S40 b) are kept off state. When it isdetected that the second threshold [RLth2] or more is larger than thefirst threshold [RLth1], a predetermined set of the switching means S1 ato S40 b is turned on again, the operation of selectively supplying thevoltage of the group node to the low voltage electric load 300 may beresumed.

It is desirable that the first threshold value [RLth1] is set to about100 kiloohms by dividing the voltage value of the high voltage powersupply of 480 V by the current value of 5 mA, which is considered tohave no effect on the human body. It is desirable that the secondthreshold value [RLth2] is set to about 1 megaohm as a resistance valuenear the middle between the [RLth1] and the insulation resistance valuethat becomes substantially infinite between the floating high voltagecircuit and the ground.

With the above configuration, the control means 200 off the switch means(S1 a to S40 b), disconnects the connection between the high voltagepower supply and the low voltage electric circuit, that is, disconnectsthe connection with the metal part of the vehicle body, it is possibleto prevent an electric shock accident by blocking the energization ofthe human body due to contact between the vehicle body and the highvoltage power supply. By surrounding the vehicle power supply device 1with a housing (not shown), it is possible to prevent the human bodyfrom directly touching the inside of the vehicle power supply device 1and receiving an electric shock.

Next, the power generation means (not shown) limits the charging voltageof the power storage element. The power generation means limits thecharging voltage so that the voltage in which the entire node of thepower storage element (1 a to 40 d) is connected in series becomes apredetermined maximum value.

On the other hand, the current consumption of the electric load 300 isnot constant, and may change significantly in a short time depending onthe operating state of the driver, for example, as in the case ofelectric power steering. In this case, if the switching means (S1 a toS40 b) are controlled by the control means 200 and the first group nodeto the 40th group node of the power storage element are switched atequal intervals, a difference may occur in the charging state of eachgroup node.

However, the control means 200 monitors the voltage of each group nodeof the power storage element via the terminals (T201, T202, T203 toT239, T240) shown in FIG. 7 . The control means 200 preferentiallyconnects the high voltage group node to the electric load 300. Then, thecontrol means 200 prevents the low voltage group node from beingconnected to the electric load 300. The control means 200 selectivelyswitches the storage element group (group node) to be discharged. As aresult, the charging state of each power storage element group (groupnode) can be kept substantially uniform.

As another embodiment, as shown in FIG. 8 , the control means 200monitors the voltage of each group node of the power storage element viathe terminals T (201, T202, T203 to T239, T240) shown in FIG. 7 . Thecontrol means 200 sets a long period during which the switching means isON for the high voltage group node. The control means 200 sets a shortperiod during which the switching means is turned ON for the low voltagegroup node. In this way, (Ton1 to Ton40) can be individually calculatedand controlled from the charge amount of the power storage element group(group node) and the current value flowing through the electric load300. As a result, each power storage element group (group node) ismaintained in a substantially uniform charging state.

As described above, as an action of the leakage detecting means 100, thepresence or absence of electric shock due to the contact of the humanbody with the high voltage portion during the period [TN] is detected.The period [TN] is a period in which the cutoff means 500, 501 shown inFIG. 4 are ON. The detection is performed depending on whether or notthe leakage resistance value of the leakage detection means 100 when thecutoff means are turned OFF is threshold value [RLth] or less and theswitch means (S1 a to S40 b) are turned OFF. Therefore, the maximum timefor the electric shock current to actually flow to the human body is[TN].

However, it is necessary that the electric shock current determined bythe voltage value of the high voltage power supply by the power storageelements 1 a to 40 d and the resistance value of the human body and thehuman body reaction expected from the duration thereof are within therange that is harmless to the human body. The duration is determined bythe [TN] time. Generally, when the current value is 30 mA and theelectric shock time is 0.1 sec or less, it is said that there is nofatal human reaction.

That is, it is said that the maximum value of the product of theelectric shock current and the electric shock time is 0.003 amperesseconds in order to suppress the reaction to a safe human body.

Therefore, in this embodiment, it is assumed that the maximum electricshock current is 100 mA from the voltage value of the high voltage powersupply of 480 V and the human body resistance of 5 KΩ. From thisassumption, the electric shock time without harm to the human body iscalculated to be 0.03 sec or less. Therefore, the maximum value of theperiod [TN] during which the cutoff means 500, 501 are ON is set to0.001 sec, which is a small value with sufficient margin.

On the other hand, it is necessary for the leakage detecting means 100to measure the leakage resistance [RLeak] during the off period [TF1],[TF2], [TF*] (* is optional) in which the control means 200 cuts off thecutoff means 500 and 501. In view of the responsiveness of a knownoperational amplifier circuit (not shown) forming the leakage detectingmeans 100, it is desirable that the off period is about 10 microseconds.

In a system equipped with the vehicle's high voltage power supply, notonly when the human body touches the high-voltage circuit part, but alsoa temporary leakage current may flow. The temporary leakage current iscaused by a leak of a mounted electronic component, a malfunction of aninsulating portion, vibration during traveling, or the like. In such acase, if the power supply from the high voltage power source to the lowvoltage electric load 300 is completely stopped by the action of thecontrol means 200, the function of each part may be lost while thevehicle is running, which may be dangerous.

Therefore, according to the embodiment of FIGS. 5 and 6 , as describedabove, when the leakage resistance value [RLeek] detected by the leakagedetection means 100 is equal to or less than the predetermined thresholdvalue [RLth], the control means 200 held the switch means (S1 a to S40b) off state for 0.5 seconds or more (Thold). After that, the controlmeans 200 turns on the switch means (S1 a to S40 b) again, or turns onthe switch means (S1 a to S40 b) again when the leakage resistance value[RLak] increases to a predetermined second threshold value [RLth2] ormore is periodically performed.

As a result, even if a temporary leakage current occurs due to a failureof each part of the vehicle body, the power supply from the high voltagepower supply to the electric load 300 is resumed. The vehicle functioncan be restored, and driving safety can be maintained. Further, thestate in which the switch means (S1 a to S40 b) are OFF is set to 0.5seconds or longer. As a result, the leakage current is not caused by thefailure of the vehicle, and even when the electric shock of the humanbody is actually caused, the fatal effect on the human body can beeliminated.

As shown in FIG. 4 , the control means 200 shortens the energizationtime [TNn] in which the cutoff means 500,501 are ON in inverseproportion to the voltage value of the high voltage power supply by thepower storage elements 1 a to 40 d. Alternatively, it is desirable thatthe energization time [TNn] is shortened in proportion to the minimumvalue of leakage resistance value [RLeak] detected by the leakagedetection means 100. As a result, if the leakage is not caused by thevehicle but is an electric shock of the human body, the higher thevoltage of the high voltage power supply, the shorter the energizationtime to the human body. And/or, the larger the electric shock current ofthe human body, the shorter the energization time to the human body. Itis more secure.

Next, in the vehicle power supply device 1 according to the embodimentof the present invention, the control means 200 switches the switchingmeans (S1 a to S40 b) and switches each group node of the power storageelement (1 a to 40 d). This switching cycle will be described withreference to FIG. 12 .

It is assumed that the control means 200 switches each group node in thecycle [T] to supply a predetermined low voltage power supply to theelectric load 300. Further, it is assumed that the power generationmeans (not shown) is constantly charging so that the total voltage ofthe power storage elements (1 a to 40 d) connected in series becomes apredetermined value.

Here, as a group node of the power storage element selected by thecontrol means 200, for example, the first group node shown in FIG. 12can be given as an example. During the ON period of the first groupnode, the current flowing through the electric load 300 causes the firstgroup node to be in a discharged state and the charging voltage drops.At the same time, since the charging current is supplied from the powergeneration means so that the total voltage of all the power storageelements 1 a to 40 d becomes constant, the voltage changes in theincreasing direction in the group node not selected. The differencebetween the maximum voltage and the minimum voltage at the specificgroup node at this time is the so-called charge/discharge depth. As thewidth of the charge/discharge depth increases, the life of the powerstorage element decreases.

However, from the viewpoint of the life of the power storage element,the time [Ton] in which the power storage element group (group node) isselectively connected to the electric load 300 by the control means 200is shortened. At the same time, it can be seen that the control cycle[T] that goes around the selection of all the power storage elementgroups (group nodes) should be shortened.

However, as shown in FIG. 10 , in the ON transition process of eachswitching means, the current [I] increases as the voltage [V] across theswitching means decreases with the ON operation when the switching meansis in the open state. At this time, in this embodiment, switching lossoccurs in the switching means S1 a to S40 b. The loss I×V at this timewhen the switching means is in the open state is as follows. Forexample, if the voltage of each group node of the power storage elementis 12V and the current of the electric load 300 is 200 A, a peak loss of12×½×200×½=600 W occurs. Further, this switching loss also occurs in theOFF transition process of the switching means.

In addition, since the switching loss occurs during the dead time [Td],the average value of the switching loss with respect to the controlcycle [T] of the control means 200 is [Td/T]. As described above, thereis a problem that the switching loss becomes excessive by shortening thecontrol cycle [T].

Further, according to the present embodiment, the voltage [VL] appliedto the electric load 300 during the dead time [Td] period shown in FIG.3 becomes 0V during the period when all the switching means (S1 a to S40b) are OFF. Therefore, since the power supplied to the electric load 300is momentarily interrupted, there is a problem that the low voltagevehicle electric load is momentarily stopped.

Therefore, as shown in FIG. 9 , the low voltage capacitor 310 isarranged in parallel with the low voltage electric load 300. As aresult, the voltage charged in the low voltage capacitor 310 continuesto be supplied to the electric load 300. From this, the voltage [VI.]does not drop to 0V, and can be limited to a slight voltage drop fromthe peak voltage as shown by the broken line [VLa] shown in FIG. 3 . Theamount of voltage drop in this case is determined by the current flowingthrough the electric load 300, the capacity of the low voltage capacitor310, and the dead time [Td]. When the dead time [Td] and the currentflowing through the electric load 300 are fixed, the larger the capacityof the low voltage capacitor 310, the smaller the amount of decrease in[VLa] can be.

The amount of drop in [VLa] is determined by the capacity of the lowvoltage capacitor 310, the dead time [Td], and the current value flowingthrough the electric load 300. Therefore, by adjusting the capacity ofthe low voltage capacitor 310 and shortening the dead time [Td], theamount of drop of the [VLa] can be reduced. Needless to say this.

Therefore, it is possible to prevent a momentary interruption of thevoltage supplied to the electric load 300. Further, in the process inwhich any of the switching means (S1 a to S40 b) transitions to the ONstate, the total voltage of the power storage elements connected inseries is 12V, and the voltage of the low voltage capacitor 310 isapproximately 12V. The total voltage of the power storage elementsconnected in series of 12V is a value at the group node of the powerstorage elements to which any switching means is turned ON andconnected. From this, the voltage across the switching means can be setto approximately 0V when the switching means is in the open state. Asshown in FIG. 11 , the switching loss in this case is such that the lossI×V becomes the minimum because the current I increases while thevoltage V remains approximately 0V.

In other words, the voltage of one group node of the power storageelement is output as the voltage supplied to the electric load 300. Itis utilized that the low voltage capacitor 310 holds the voltage of thegroup node. If the voltage of each group node is the same, the voltageof each group node when switching all the group nodes and the voltage ofthe electric load 300 (low voltage capacitor 310) are the same. Theoperation of the switching means is so-called [ZVS] (known zero voltswitching), and theoretically no switching loss is generated.

According to this embodiment, since the switching loss is not generatedat the time of stepping down from the high voltage power supply to thelow voltage power supply, the heat loss generated by the switchingelement used for stepping down is extremely reduced. In the experimentsof the inventors, when a step-down device having an output of 2.5 kW wasmanufactured, the power conversion efficiency was 99.5%. The heat sinkis no longer required, which makes it possible to significantly reducethe system cost.

In this embodiment, as described above, the control means 200 measuresthe insulation resistance value between the high voltage portion and theground by the leakage detecting means 100 during the period when thebreaking means 500 and 501 are turned off.

In this case, the power supply from the high voltage power supply to thehigh voltage load device 400 is stopped for prescribed period. As shownin FIG. 2 , it is preferable that the high voltage capacitor 700 has asufficient capacitance is placed in parallel so that the specifiedvoltage can be supplied from the high voltage capacitor to the highvoltage load device 400 even during the stop period.

Further, by disposing the high voltage capacitor 700, it is possible toreduce the switching loss of the cutoff means 500 and 501 which areperiodically interrupted. This is the same reason that the switchingloss generated in the switching means can be reduced by adding the lowvoltage capacitor 310, and thus detailed description thereof will beomitted.

Next, as another embodiment, as shown in FIG. 13 , capacitors (601, 602to 640) are connected at both ends of each power storage element group(group node) formed by connecting four nodes in series among the powerstorage elements 1 a to 40 d.

It is known that the power storage element has an equivalent seriesresistance value of several tens of mΩ as an internal resistance (notshown) when, for example, a lithium ion battery is adopted. Therefore,in the case of four power storage elements connected in series in onegroup node in the present embodiment, each group node of the powerstorage element has an internal resistance of about 100 ma

As shown in FIG. 3 , the voltage [VL] of the electric load 300 riseswhen one of the switching means is turned ON after the dead time [Td] isterminated. At this time, the electric time constant of the risingportion is represented by the product of the capacitance of thecapacitor 310 and the above-mentioned internal resistance.

Therefore, when the capacitor 310 is charged by the internal resistanceof the power storage element, the rising waveform [VLb] of [VL], asshown in FIG. 3 , has a large time constant and the low voltage statecontinues for a long time. Further, since this is repeated in the period[T], it becomes a factor that the average value of the voltage suppliedto the electric load 300 decreases. It is desirable that the timeconstant be as small as possible.

Generally, the equivalent series resistance of a capacitor as acapacitance element is as small as several mΩ. Therefore, if a capacitor(601, 602 to 640) is connected in parallel with each group node of thepower storage element as in the present embodiment, the internalresistance of the power storage element is apparently reduced. As shownin FIG. 3 , the rising waveform [VLc] of [VL] when the capacitor 310 ischarged by the internal resistance has a small time constant and the lowvoltage state becomes short. Since this is repeated in the period [T],the decrease in the average value of the voltage supplied to theelectric load 300 is small, and the accuracy of the voltage supplied tothe electric load 300 is improved.

Hereinafter, a method of outputting AC power for supplying to a deviceoperated by a commercial power source from a plurality of power storageelements connected in series to form a high voltage power source will bedescribed. FIG. 14 is referenced. Since the basic configuration issimilar to the above-described embodiment, the figure showing theconfiguration in this embodiment is omitted.

First, as the power storage element, 180 lithium ion batteries having acell voltage of 3V unit are connected in series, and the total voltageis set to 540V. Next, the 60 power storage elements are regarded as onegroup node, and the whole is divided into three group nodes (G1 to G3).The voltage of each group node is switched every 1 ms by the switchingmeans and supplied to the commercial power supply load. When 10 ms haselapsed, the selected group node is G1. Next, when G2 is selected andsupplied to the commercial power load, the switching means is operatedto connect to the commercial power load. The polarity of the powerstorage element group (group node) is reversed. Subsequently, whenswitching between G3 and G1 while maintaining the same polarity, andfinally when G3 is selected and connected in the next cycle in which G2is selected, the power storage element group (group node) of which thepolarity is reversed when connecting to the commercial power load again.

By repeating the above operation, a rectangular AC voltage of 50 Hz, ±90V can be applied to the commercial power supply load.

As described above, in the vehicle power supply device according to theembodiment of the present invention, the high voltage power supply isformed by connecting power storage elements in series. By selectivelyconnecting a predetermined power storage element group (group node) fromthe high voltage power source to a low voltage electric load, powerconversion from high voltage to low voltage can be performed. At thattime, by switching the power storage element group (group node) at highspeed, the charge/discharge depth of the power storage element isreduced and the life is improved. At the same time, the switching lossof the switching means for switching can be made substantially zero. Ithas an excellent feature that the weight and cost of the member requiredfor heat dissipation of the switching element can be significantlyimproved.

In addition, the leakage resistance value is measured with the highvoltage circuit temporarily cut off by the cutoff means, and if adecrease in the resistance value is observed, it is assumed that thehuman body is touching the high voltage circuit part, and cutting theconnection between the high voltage power source and the low voltageelectric circuit connected to the vehicle body continuously or for aspecified period of time. A dangerous human reaction during electricshock can be suppressed even without using means such as an isolatedDC-DC converter.

As another embodiment, as shown in FIG. 15 , by exchanging the powerstorage element and the electric load in the above-described embodiment,the voltage of the electric storage means can be boosted and supplied tothe electric load. This is a matter that can be easily conceived by aperson having ordinary knowledge in the technical field to which thepresent invention belongs. In the embodiment shown in FIG. 14 , acapacitor constitutes a node and by charging each node with the voltageof the power storage element via the switch means, it is configured totake out the boosted power from the capacitors connected in series.

Further, also in this embodiment, the cutoff means is added to the highvoltage side connected to the electric load means, and the resistancevalue between the grounds on the high voltage side is measured by theleakage detecting means in the same manner as in the above embodiment.When an electric shock to the human body is measured, it is possible toprevent an electric shock accident by shutting off the switching meansfor selectively connecting each node.

INDUSTRIAL APPLICABILITY

In the embodiment of the present invention, only a limited configurationand operation are shown as examples. The number of power storageelements connected in series, the type of power storage element, theelement type and configuration of the switching means, the type of thecutoff means, the number of the cutoff means, location of the cutoffmeans, whether or not there is synchronization between the intermittentcycle of the cutoff means and the intermittent cycle of the switchingmeans and the operation timing of the control means can take any form.At the same time, it should be easily understood that various knowntechniques exist as the configuration of the leakage detecting means,and that various failure detecting means and a fail-safe function at thetime of failure may be added.

DESCRIPTION OF NUMERICAL REFERENCES

-   1 a to 1 d power storage element (node)-   S1 a to S40 b switching means-   100 Leakage detection means-   200 control means-   300 electrical load-   400 high voltage load device-   500, S01 cutoff means

1. A power supply device for a vehicle, comprising: an electric loadthat operates at a predetermined low voltage; a high-voltage powersupply that provides a high-voltage DC power supply by connecting inseries a plurality of power storage elements constituting nodes thatsupply said predetermined low voltage; a high-voltage load deviceconnected to the high-voltage power supply via a wire harness; aplurality of switch means provided corresponding to said nodes thatsupply the predetermined low voltage to the electric load; a controlmeans wherein the control means supplies a voltage by turning on atleast one of the switch means for supplying the voltage from at leastone node and turning off the other switch means for supplying thevoltage from the other nodes, and after setting a dead time period toturn off all the switch means once, sequentially repeating turning on anext one of the switch means of a next node that supplies the voltagenext and turning off the other switch means that supply the voltage fromthe other nodes so that the voltage is supplied from all the storageelements; a cutoff means for cutting off an electric circuit between thehigh-voltage power supply and the high-voltage load device; and aleakage detection means that detects a leakage resistance between anelectric circuit part constituted by the high-voltage power supply andthe high-voltage load device and a ground potential and sends a signalto said control means, wherein the control means determines the signaltransmitted from the leakage detection means during the period when thecutoff means is off, and when the leakage resistance is equal to orlower than a predetermined value, all the switch means are kept an offstate for a predetermined period of time.
 2. The power supply device forthe vehicle according to claim 1, wherein in said high-voltage powersupply, (n (n: natural number)×N (N: natural number)) of said powerstorage elements constituting the nodes, in which n pieces of the nodesmake up the predetermined low voltage, are connected in series, wherebya DC power source having a high voltage N times higher than thepredetermined low voltage is obtained.
 3. The power supply device forthe vehicle according to claim 1, wherein said control means controlsthe switch means so as to periodically change a plurality of selectednodes.
 4. The power supply device for the vehicle according to claim 3,wherein said control means determines a node to be selected so thatcharge/discharge states of the plurality of power storage elementsbecome substantially uniform.
 5. The power supply device for the vehicleaccording to claim 3, wherein said control means determines a selectiveholding time of each node so that charge/discharge states of theplurality of power storage elements become substantially uniform.
 6. Thepower supply device for the vehicle according to claim 1, wherein a timefor connecting said high-voltage power supply to said high-voltage loaddevice by said cutoff means is set so that a time during which thecurrent flows from the high voltage power supply to a human body is lessthan a time during which an electric shock accident is caused in thehuman body.
 7. The power supply device for the vehicle according toclaim 6, wherein said time for connecting said high-voltage power supplyto said high-voltage load device by said cutoff means is set so as to bea time which is inversely proportional to a voltage value of the highvoltage power supply, or a time which is proportional to the leakageresistance value detected by the leakage detecting means.
 8. The powersupply device for the vehicle according to claim 1, wherein said controlmeans fixes all the switch means to the off state when a leakageresistance value of said leakage detection means is equal to or lowerthan a predetermined value.
 9. The power supply device for the vehicleaccording to claim 1, wherein when a leakage resistance value of theleakage detection means is equal to or lower than a predetermined value,said control means repeats an operation of holding a state in which allthe switch means are off for a predetermined time and subsequentlyselectively connecting said each node and said electric load by theswitch means.
 10. The power supply device for the vehicle according toclaim 1, wherein said control means repeats an operation in which: whena leakage resistance value of the leakage detection means is equal to orlower than a first threshold value, said control means turns off theswitch means, when a leakage resistance value of the leakage detectionmeans is equal to or higher than a second threshold value which islarger than the first threshold, said control means turns on the switchmeans.
 11. The power supply device for the vehicle according to claim 1,wherein said control means controls said cutoff means so that a productof a period in which said high-voltage power supply and saidhigh-voltage load device are connected by said cutoff means and thecurrent flows from the high-voltage power supply to a human body is0.003 amperes×1 second or less.
 12. The power supply device for thevehicle according to claim 1, wherein said control means sets a cyclefor switching a node selected by said switch means to be a predeterminedvalue or less so that a magnitude of a charge/discharge depth in eachnode of the power storage elements is equal to or less than apredetermined value.
 13. The power supply device for the vehicleaccording to claim 1, wherein a low voltage capacitor is connected inparallel with the electric load.
 14. The power supply device for thevehicle according to claim 1, wherein a high voltage capacitor isconnected in parallel with said high-voltage load device.
 15. The powersupply device for the vehicle according to claim 13, wherein said deadtime period or a capacitance value of the low voltage capacitor is setso that a voltage drop width applied to the electric load during thedead time period is not more than a predetermined value.
 16. The powersupply device for the vehicle according to claim 14, wherein an offperiod of said cutoff means or a capacitance value of the high voltagecapacitor is set so that a voltage drop width applied to thehigh-voltage load device during the off period of said cutoff means isnot more than a predetermined value.
 17. The power supply device for thevehicle according to claim 13, wherein the capacitor is arranged inparallel with each node of said power storage elements.
 18. The powersupply device for the vehicle according to claim 1, wherein from eachnode of the high-voltage power supply that provides said high-voltage DCpower supply by connecting in series said power storage elements, an ACpower is supplied to the electric load by alternately reversing apolarity with a high potential side and a low potential side atpredetermined periods when the electric load is connected by the switchmeans.